The purpose of this project is three-fold: First, to analyze quantitatively intracortical projection patterns for populations of cells in mouse somatosensory cortex from focal HRP injections in vitro. The goal is to identify anatomical substrates for local directional biases which have been demonstrated functionally within rodent somatosensory cortex. Second, to characterize quantitatively patterns of intracortical connectivity in mice with infraorbital nerve (ION) lesions (peripheral deafferentation) in the postnatal period. The goal is to define the critical period for development of normal connection patterns between barrel cortical neurons. Third, to characterize quantitatively patterns of intracortical connections after chronic whisker clipping (chronic sensory deprivation) and after the whiskers have been allowed to grow back to reverse the sensory deprivation. The goal is to determine whether or not appropriate patterned input from the sensory periphery is necessary for development and maintenance of normal intracortical connections. Recently templates have been developed in our laboratory to allow accurate localization of barrel cortex for extracellular HRP injections in fresh flattened mouse cortex. in pilot studies, focal injections into individual cortical barrels yield HRP-filled fibers and cells in adjacent barrels. Our intent is to analyze the distribution of labeled cells in these adjacent barrels in relation to the injection sites. This will be accomplished by recording cell locations (x,y,z coordinates) within the cortex with a computer microscope equipped with a motorized stage, image processor and advanced statistical package. Sections of a given hemisphere will be stacked, one on top another, and reconstructed with computer-assisted image processing methods to yield a three dimensional representation of labeled cell bodies. I am looking for a directional bias in the anatomical substrate to correlate with functional biases previously demonstrated with physiological and metabolic (i.e. 2-DG) techniques. As my results will be quantitative I should be able to formulate and statistically test hypotheses concerning vertical and horizontal connectional tendencies within this anatomically distinct cortex. Quantification will also allow objective comparison of results between the three experimental groups and the significance of any differences between them to be established. This computer-assisted analysis of cortical connectional patterns in normal and experimentally manipulated animals will provide insight into the organization, development and maintenance of intracortical connections.